Morning Serum Cortisol Level Predicts Central Adrenal Insufficiency Diagnosed by Insulin Tolerance Test

Abstract

<b><i>Introduction:</i></b> According to guidelines, a morning serum cortisol level &#x3c;83 nmol/L is diagnostic for central adrenal insufficiency (CAI), a value &#x3e;414 nmol/L excludes CAI, while values between 83 and 414 nmol/L require stimulation tests. However, there are no currently reliable data on morning serum cortisol for prediction of cortisol response to insulin tolerance test (ITT). <b><i>Objective:</i></b> Using the receiver-operating characteristic curve analysis, the purpose of this study was to detect the morning serum cortisol cutoff with a specificity (SP) or a sensitivity (SE) above 95% that identify those patients who should not be tested with ITT. <b><i>Methods:</i></b> We included 141 adult patients (83 males) aged 42.7 ± 12.3 (mean ± standard deviation) years old. Based on the serum cortisol response to ITT, patients have been divided into 2 groups: subjects with CAI (peak serum cortisol &#x3c;500 nmol/L; 65 patients) and subjects with preserved adrenocortical function (peak cortisol &#x3e;500 nmol/L; 76 patients). <b><i>Results:</i></b> The best morning cortisol cutoff, in terms of SE (87.7%) and SP (46.1%), was ≤323.3 nmol/L. The cutoff of morning serum cortisol concentration that best predicted a deficient response to ITT was ≤126.4 nmol/L (SE 13.8%, SP 98.7%). The cutoff of morning serum cortisol concentration that best predicted a normal response to ITT was &#x3e;444.7 nmol/L (SE 96.9%, SP 14.5%). <b><i>Conclusions:</i></b> This is the first study that identifies a morning serum cortisol cutoff that best predict the response to ITT in order to simplify the diagnostic process in patients with suspected CAI. A new diagnostic flow-chart for CAI is proposed.